Officers said they were also keen to trace a man seen walking near the victim's house at about 21:40 GMT on 20 March.

He was wearing a high visibility sleeveless top and is thought to have walked past a nearby car wash.

Kent Police said both the man and the group of workmen may have information crucial to the investigation.

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Mr Blackman's body was found at his home on 21 March

On Thursday, Mr Blackman's family paid tribute to him. "It is unthinkable to us that a vulnerable 73-year-old alone in his home could be harmed," they said.

"We truly can't believe that we won't see him again or hear his laughter and we will never come to terms with the manner of his death."

The family described Mr Blackman, a self-taught car mechanic who set up his own garage, as a man who lived a simple life without extravagance and who had desperately missed his wife after her death from cancer six years ago.

They said the couple would have celebrated their golden wedding anniversary this July.